expression()

Hi,
I'm trying to use expression() to write a text to a graphic in the  
margin.

Using:

mtext(expression(beta),side=1,line=2)

writes a perfect beta greek character, but I need to add a subindex
"max", and I'm trying:

mtext(paste(expression(beta),"max"),side=1,line=2)

simply writes "beta max" in the plot.

Please, Could you tell me what I'm doing wrong?

By the way, is there a way to add Latex expressions to graphics?  
Then I
could use the Latex expression: $\beta_{\mathrm{max}}$. This also  
would
be very useful for me for more complex expressions in plots.

Best regards,

Javier

-- 
Javier Garc?a-Pintado
Institute of Earth Sciences Jaume Almera (CSIC)
Lluis Sole Sabaris s/n, 08028 Barcelona
Phone: +34 934095410
Fax:   +34 934110012
e-mail:jgarcia at ija.csic.es